AC_FUNC_FSEEKO and optional execution

[Russ Allbery]

Old (but still occasionally seen) BSD systems (I forget which varient)
didn't have fseeko/ftello but did have an fgetpos and fsetpos that worked
with 64-bit offsets.  INN provided some compatibility code for those
systems that implemented fseeko and ftello in terms of fgetpos and
fsetpos, well enough for INN's purposes.

Currently, this is done with:

    AC_FUNC_FSEEKO
    if test x"$ac_cv_func_fseeko" != xyes ; then
        INN_TYPE_FPOS_T_LARGE
        AC_CHECK_DECLS([fseeko, ftello])
        AC_LIBOBJ([fseeko])
        AC_LIBOBJ([ftello])
    fi

This stopped working with recent Autoconf (I think around 2.62, but I
could be wrong).  AC_FUNC_FSEEKO used to set ac_cv_func_fseeko but
stopped; now ac_cv_sys_largefile_source is set instead (and not to
something as simple as yes or no).

This is exactly why I hate relying on cache variables.  :)

Could AC_FUNC_FSEEKO acquire ACTION_IF_FOUND and ACTION_IF_NOT_FOUND
arguments so that I can implement this conditional probing and AC_LIBOBJ
calls in a sane fashion without relying on undocumented and unsupported
macro internals?

-- 
Russ Allbery (address@hidden)             <http://www.eyrie.org/~eagle/>